Method of flexure mounting print hammers



Aug. 8, 1967 H. M. SHNEIDER ETAL 3,334,409

METHOD OF FLEXURE MOUNTING PRINT HAMMERS Filed Sept. 1, 1964 INVENTORS. HAROLD M. SHNE/DER SIDNEY E. SMITH BY Lazy ATTORNEY.

United States Patent 3,334,409 METHOD OF FLEXURE MgUNTING PRINT 8 Claims. (Cl. 29-428) The present invention relates to a new method of flexure-mounting print hammers to provide a hammer module for an impact printer.

It is well known in the printer art to support print hammers on flexure mounts. A hammer mount of this type may include a pair of flexure springs taking the form of resilient foils which support the front and rear portions of the print hammer on a stationary base. The flexure springs will usually urge the print hammer to a rest position determined by a backstop. When the hammer is struck from the rear by an actuator, it is driven forward into contact with a platen, e.g. with a rotating character-bearing print roll, to effect printing on an intermediately positioned paper web.

Lateral rigidity, i.e. resistance to sidewise motion of the print hammer, is important for proper print-out. This is particularly the case where the print roll contains a plurality of closely spaced, adjacent columns of characters, each column having a corresponding print hammer positioned opposite it. Lateral rigidity must be combined with complete flexibility in the forward and backward directions to enable each print hammer to perform its intended function without interference. These operating requirements apply not only to the flexure springs, but also to the means whereby they are fastened to the print hammer and to the base respectively. In effect the springs must be flexibly attached to these components, yet resist lateral movement. The fastening means must also be able to withstand repeated use without deterioration in order to avoid damage to the print hammer or to the rotating print roll.

Prior art flexure mounts used in connection with print hammers fall short in various respects of attaining the above-discussed operating characteristics. Where the flexure springs are bolted to the base and to the hammers, as may be the case in a very simple mounting arrangement, stress concentrations will result during use, particularly in the hammers which are relatively small so that the bolts cannot penetrate deeply. Such stress concentrations can be avoided by bonding the component parts together. Arrangements of this kind have, however, enjoyed only a moderate degree of success in the past. Bonding materials such as rubber, which have great flexibility, could not heretofore be made to adhere to metal for prolonged periods of use. Plastic, which is generally used as the bonding agent, exhibits an undesirable amount of resistance to the flexing required during the forward and backward hammer movement.

In one commonly used prior art arrangement, the base is embedded in a block of plastic, together with the end portions of the flexure springs which are bent around the base and are bonded or bolted thereto. Quite apart from the fact that such an arrangement is relatively expensive to implement, the flexure springs protrude from grooves in the plastic block and exert a rolling action on the latter while flexing. This action has a deteriorating eifect on the plastic and shortens the useful life of the flexure mount.

Difliculties have also been encountered in prior art devices in aligning the print hammers with each other. Attempted solutions of this problem have materially raised the cost of fabrication. Proper hammer alignment are flexure-mounted on a single base to form a hammer 3,334,409 Patented Aug. 8, 1967 module. Any alignment variations will result in positional variations of the printed characters relative to the print line. Similarly, the hammers must be aligned with the columns of type characters of the print roll in order to obtain a proper print-out and hence the spacing of successive hammers must also be accurately maintained.

It is the primary object of the present invention to provide a method of flexure-mounting print hammers on a common base to form print hammer modules which are not subject to the foregoing disadvantages.

It is another object of the present invention to provide a method of flexure-mounting print hammers wherein lateral rigidity of the print hammers is obtained and stress concentrations in the metal are avoided.

It is a further object of the present invention to provide a method of flexure-mounting print hammers wherein a bond is employed between the flexures and the print hammers and the base respectively, which can withstand prolonged and repeated use.

It is an additional object of the present invention to provide a method of flexure-mounting print hammers wherein a flexible bond between the flexure springs and the hammers and base respectively is employed which does not interfere with the forward or backward movement of the print hammers.

It is still another object of the present invention to provide a simple and economical method of flexuremounting a plurality of print hammers on a single base in alignment with each other.

It is still a further object of the present invention to provide a simple and economical method of flexuremounting a plurality of print hammers on a single base at an accurately maintained mutual hammer spacing.

The foregoing objects of the present invention, together with the features and advantages thereof will become apparent from the following detailed specification, when read with the accompanying drawings in which:

FIGURE 1 illustrates a preferred embodiment of a flexure mount which is fabricated in accordance with the present invention;

FIGURE 2 illustrates a step in the process of fabricating the apparatus of FIGURE 1;

FIGURES 3 and 4 illustrate another step in the fabrication of the apparatus of FIGURE 1; and

FIGURE 5 illustrates in detail a portion of the flexure mount of FIGURE 1.

With reference now to the drawings, a preferred embodiment of the present invention is illustrated in FIG- URE 1. A pair of print hammers 10 and 12 are mounted on a single base 14, each hammer being supported by a pair of flexure springs, or fiexures, in the form of substantially rectangular foils 16, 18 and 20, 22 respectively. The flexure spring 16 has a pin 24a joined thereto at one end and a pin 26 joined to its other end. The pin 24a has a length equal to the width of the print hammer 10 and is centrally supported in a hole 28 by a rubber bond 30 which fastens the pin to the internal surfaces of the hole.

The hole 28 runs the width of the hammer 10 and has associated therewith a slot 32 which similarly traverses the width of the hammer 10 and communicates between the hole 28 and an external hammer surface 34. The slot 32 has a pair of parallel side walls spaced from each other a distance that is less than the diameter 28 in the preferred embodiment illustrated. The rubber bond 30 is also present in the slot and bonds the flexure spring 16 to the surfaces of the latter. The rubber further forms an external bond 36 between the upper end portions of the spring 16 and the exterior hammer surface 34, substantially triangular in cross-section with the base of the triangle exceeding the width of the slot 32.. The bond 36 extends the entire width of the flexure spring and of the print hammer 18 which are substantially coextensive in width.

The lower end portion of the spring 16 is fastened to the base 14 in similar manner. The pin 26, which has a length coextensive with the width of the base 14, is centrally positioned in a hole 40 which similarly traverses the width of the base. The pin 26 is rubber-bonded to the interior walls of the hole 48. A slot 42, which extends the entire width of the base 14, communicates between the exterior base surface 44 and the hole 48. In the preferred embodiment illustrated, the slot 42 has parallel walls spaced from each other a distance less than the diameter of the hole 48. The lower end portion of the flexure spring 16 is bonded to the interior surfaces of the slot by means of rubber which further forms an external bond 46 between the the flexure spring and the base surface 44. The latter bond is similar to the bond 35, having a substantially triangular cross-section and running the width of the flexure spring.

The upper end of the flexure spring 29 is joined to a pin 24b centrally positioned in the hole 48 of the hammer 12, while the lower end of the latter spring is joined to the pin 26 which traverses the width of the base 14. The flexure springs 16 and 28 thus form a group of two having their lower ends joined to a common pin.

In a similar manner, the flexure springs 18 and 22 constitute a group of two, having their lower ends joined to a common pin56, which traverses the width of the base 14 and which is centrally positioned in a hole 58 that similarly runs the entire width of the base. The upper ends of the springs 18 and 22 are joined to a pair of pins 58a and 50b respectively, which are centrally positioned in a pair of holes 52 and 54 respectively, each traversing the width of its corresponding print hammer. The holes 48, 52, 54 and 58 have corresponding slots 68, 62, 64 and 66 respectively associated therewith, each slot communicating between an exterior surface and its corresponding hole and having parallel walls spaced a distance less than the diameter of the corresponding holes in the embodiment shown. The base 14 further includes a threaded bore 68 for mounting purposes.

The print hammers and 12 are substantially identical and further include convex rear impact surfaces 63 and 65 and concave striking surfaces 67 and 69 respectively. The latter surfaces are adapted to confront respective character columns of the print roll when the base 14 is mounted in operating position by means of a screw engaging the bore 68. Rearwardly positioned actuators may then selectively drive the hammers forward against the print roll to effect printing on an intermediately positioned paper web.

As previously explained, the print hammers must be accurately aligned with each other so that the printed characters will display no positional variations relative to the print line. Moreover, the mutual spacing of the hammers must be accurately maintained so that each hammer directly confronts its corresponding character column of the print roll when the base is mounted in operating position. To this end, the hammers and the base are first fabricated with the aforesaid holes and slots, which may be provided either by stamping out these parts or by machining them to the desired form.

FIGURE 2 illustrates the step of assembling the flexure springs and their associated pins with reference to the group of springs 16 and 20. The flexure springs are seen to be substantially identical and to have a rectangular configuration. The springs are positioned in a common plane and are spaced from each other in accordance with the desired mutual spacing of the print hammers. The upper and lower spring ends are seen to be aligned with each other.

A first pair of wires 24 and 24", each having a substantially semicircular cross-section, is positioned on opposite sides of the flexure springs, with the fiat wire surfaces facing the springs. The upper spring ends are aligned with the upper edges of the wires. Similarly, a pair of wires 26' and 26 is positioned at the lower ends of the flexure springs on opposite sides of the latter and with the flat wire surfaces facing the springs. Again, the lower wire edges are aligned with the lower spring ends. It will be noted, that the wires extend on both sides beyond the flexure springs which are centrally positioned along the wires.

The flexure springs are soldered to the wires in the relative positions shown in FIGURE 2. A group of two spaced, aligned flexure springs is thus provided, whose upper and lower ends are joined to a pair of common pins 24 and 26 respectively. The procedure outlined hereinabove is similarly applicable to the group of flexure springs 18 and 22. The latter are aligned in spaced relationship in a common plane and have their upper and lower ends joined to a pair of common pins 50 and 56 respectively.

The next step in the method of flexure-mounting the print hammers is to coat the interior surfaces of the holes and of the slots with a rubber-adhesive substance, e.g. by painting it on. Exterior surfaces are coated only in the vicinity of the slots where the flexure spring ends are received, e.g. the surface 34. The aforesaid spring ends and the pins joined thereto are similarly coated with a rubber-adhesive substance.

FIGURES 3 and 4 illustrate the method of inserting the component parts of the flexure mount herein described into an injection mold 70 which operates in conjunction with a mating cover '72. The injection mold contains suitable cavities for receiving the base, the spaced print hammers and the flexure springs. Triangular cavity extensions 71, 73, 75 and 77 are provided, which merge the flexure cavities into the base and print hammer cavities respectively. The mold 70 further includes a threaded bore 82. The mold and the cover 72 include mutually aligned bores for accurately locating the aforesaid pins. Aligned bores 74, 76 and 78, 80 are shown in FIGURE 3 for receiving the pins 50 and 56.

With the cover 72 removed, in FIGURE 3, the two groups of connected springs are placed into the injection mold 70, with the pins inserted in their respective bores. The base 14 is next placed into the appropriate cavity of the mold. This is done by sliding the holes 58 and 40 of the base over the pins 56 and 26 respectively. Simultaneously the slot 66, which extends the width of the base 14, is slipped over the group of flexure springs 18 and 22, while the slot 42 is slipped over the group of flexure springs 16 and 20. When the base is in position, both groups of flexure springs extend from the two base slots 42 and 66 and the threaded bores 68 and 82 are aligned. A screw inserted from outside the mold and engaging both of the latter bores, will then accurately hold the base in position within the mold.

The hammer 12 is next inserted into the mold by sliding the holes 48 and 54 thereof over the pins 24 and 50 respectively. During this operation, the hammer slot 64 is first passed over the flexure spring 18 and then over the spring 22 which protrudes from the slot 64 when the hammer 12 is properly positioned. At the same time, the slot 60 is slipped over the flexure springs 16 and 20 so that the latter spring protrudes from the slot 60 in the final hammer position. A piece of shim metal 84 is placed on top of the hammer 12 and the hammer 10 is subsequently inserted. The shim 84 precisely determines the spacing between the hammers 10 and 12. The insertion of the hammer 10 occurs by sliding the hammer holes 28 and 52 over the pins 24 and 50 respectively and by simultaneously sliding the corresponding hammer slots 32 and 62 over the flexure springs 16 and 18 respectively. The latter pair of springs will protrude from the slots 32 and 62 respectively when the hammer 10 is in position.

When all the parts have been accurately positioned within the injection mold 70, the cover 72 is placed in position so that the bores 86 and 76 in the cover are engaged by corresponding pins 50- and 56 respectively. The cover 72 further includes injection bores, such as the bores 79 and 81, through which liquid rubber is forced. The last-mentioned bores are located in the vicinity of the aforementioned holes in the print hammers and the base.

Rubber is then injected under pressure to fill the voids within the mold. These voids include the spaces between each pin and the interior surfaces of the hole in which the pin is located, as well as the space between each fiexure spring and the interior surfaces of the slot communicating with the aforesaid hole. Additionally, the injected rubber flows into the triangular spaces 71, 73, 75 and 77 which communicate between the aforesaid slots and the external surfaces of the hammers and the base. Because of the previously applied rubber-adhesive substance, a firm bond is established between the aforesaid surfaces of the components and the pins and flexure springs.

After the rubber is injected, it is vulcanized within the mold by the application of heat. The cover 72 as well as the screw which engages the bores 68 and 82, are subsequently removed. The components, now bonded into a complete flexure mount, are then lifted from the mold. Any excess rubber deposited during the injection molding process in areas to which no rubber-adhesive substance was applied, is readily stripped off at this time. The shim 84 is removed from its position between the hammers and 12 and the pins 50 and 24 are out apart between the hammers to form separate pins 50a, 50b and 24a, 24b respectively. Each hammer is now freely supported on its corresponding pair of flexure springs. Portions of the pins which protrude from the print hammers 10 and 12, as well as portions of the pins 26 and 56 protruding from the base 14, are then machined olf.

The above-described method provides a print hammer fiexure mount that is superior to devices of this kind heretofore in use. Each bond which fastens a flexure spring to a print hammer or to the base is truly flexible due to the nature of the bond as well as the rubber bonding material employed. As a consequence, no interference with the forward and backward print hammer movement is encountered.

FIGURE 5 illustrates the action of a rubber bond during the forward movement of the print hammer 10. It will be seen that the portion of the flexure spring 16 within the slot is urged toward the rear slot wall. This is made possible by the elasticity of the rubber which is compressed to the rear of the spring and is stretched in front of it. This action is even more prominent in the external bond portion 36 which fastens the flexure spring 16 to the external surface 34. It will also be noted from FIGURE 5 that no rolling of the bond 36 occurs during the flexing of the spring 16 which could deteriorate the bond. The presence of the pins joined to the end of each flexure spring assures lateral rigidity. In the base, where such rigidity is primarily required, the pins 26 and 56 traverse the entire base width.

Owing to the configuration of the rubber bond in the preferred embodiment shown, the rubber tends to remain in place even if it should work loose from the surfaces to Which it is bonded. Thus, because the width of the slot 32 in FIGURE 5 is smaller than the diameter of the hole 28, the rubber in the latter cannot slip down through the slot if it were to come loose from the interior walls. This action is supported by the external bond portion 36 which cooperates with the internal bond to grip the hammer and to prevent the pin from sliding upward under the aforesaid conditions. As a consequence, the pin 24a, and hence the flexure springs 16, are held in the hole 28 under these conditions and possible damage to the print hammer or to the print roll is averted. Although during the operation of the print hammer there is little tendency for the pin 24a to slip out of the hole 28 in an axial direction should the bond work loose, such action can readily be prevented by countersinking the hole 28 at both ends. The rubber bond in the hole, being wider at both ends than in the middle, will then remain in place.

The method of flexure-mounting print hammers which forms the subject matter of the present invention provides a hammer module which has operating characteristics superior to those of heretofore available modules. The method is simple and economical to implement and alfords accurate alignment and spacing of the print hammers mounted on the same base. As many as 66 modules of the type illustrated in FIGURE 1 have been successfully used in a high-speed printer. Since the modules are readily adjustable on their individual mounts, the relative spacing and alignment of all the print hammers are easily carried out.

The above-described and illustrated invention is subject to different variations, depending on the requirements of each particular situation. For example, a single base may support a group of print hammers numbering more than two. Nor need the different components have the precise configuration shown in the drawing. Thus, a group of flexure springs, such as 18 and 22, may be stamped out of a single sheet of metal and left connected at the end which is submerged in the base. Similarly, the hammers may vary from those illustrated in the drawings. This also applies to such parts as the pins which may have a different crosssectional configuration from that shown.

Numerous modifications, departures and substitutions will now occur to those skilled in the art, all of which fall within the scope contemplated by the present inventron. Consequently, the invention herein disclosed is to be construed as limited only by the spirit and scope of the appended claims.

What is claimed is: 1. The method of mounting a plurality of spaced print hammers on a base, each of said hammers being supported on a pair of fiexures, comprising the steps of fabr cating said print hammers and base respectively with transverse holes and corresponding externally open slots communicating with said holes, said holes and slots extending the width of said base and print hammers respectively, arranging said flexure pair of parallel pins each having length in excess of said base width, coat ng said holes, slots, pins and the end portions of sa d tlexures with a rubber-adhesive substance pos tioning each group of joined flexures in an injecincluding 1 accepting said base, said print ures,

positioning said base in said mold by sliding the holes over said pins and flexures respecflexures to said pins in each group comprises the steps of positioning the spaced, aligned fiexure ends of each set between the flat surfaces of a pair of wires of substantially semicircular cross-section,

and soldering said ends to said wire pairs to form said pair of parallel pins each common to the ends of one group.

3. The method of mounting a print hammer on a base by the use of fiexure means having opposite ends, comprising the steps of fabricating said print hammer and base with holes and corresponding slots communicating with said holes, said holes and slots running the Width of said base and print hammers respectively,

attaching said opposite ends of said fiexure means to separate pin means each having a predetermined length greater than said base width,

coating the surfaces of said holes, slots, pin means and the end portions of said fiexure means with a rubberadhesive substance,

inserting said pin means in an injection mold having bores for accurately locating the same and further including preformed cavities for accepting said attached fiexure means, said base and said print hammer,

placing said base and print hammer into said mold by passing said holes over the corresponding pins to a position wherein said fiexure means extend through said slots in alignment therewith,

injecting rubber under pressure into said mold in the vicinity of said holes to bond said pins and fiexure means to said holes and slots,

vulcanizing said rubber,

and removing the bonded parts from said mold and machining off protruding pin portions. 4. The method of mounting a plurality of spaced print hammers on a single base, each hammer being supported on a pair of flat fiexure springs, comprising the steps of fabricating each of said print hammers and said base with a pair of spaced holes and with corresponding slots, each slot having parallel walls and communicating between an external surface and a hole, said holes and communicating slots traversing the width of said base and print hammers respectively,

arranging said fiexure springs in two substantially identical groups each positioned in a plane spaced in accordance with the desired spacing of said print hammers and with their corresponding ends aligned,

positioning each set of corresponding spring ends in each plane between the flat surfaces of a pair of wires of substantially simicircular cross-section, each of said wires having a predetermined length in excess of the width of said base,

soldering each set of spring ends to said wire pairs to form a pair of parallel pins connecting opposite ends in each group of springs painting said external surface, the interior surfaces of said holes and slots, said pins and the end portions of said fiexure springs with a rubber-adhesive compound, inserting each of said groups in an injection mold opening to one side, said mold having bores for accurately locating said pins and further including preformed cavities for accepting said base, said print hammers and said fiexure springs respectively, the cavities for said fiexure springs merging into said base and print hammer cavities respectively,

placing said base in said mold by sliding its pair of holes andcorresponding slots over the appropriate pins and springs respectively to a position where said fiexure springs extend from said slots,

placing said print hammers in said mold interleaved with shim metal spacers by sliding each pair of print hammer holes and the corresponding slots over appropriate pins and springs respectively to a position Where each hammer is aligned with a pair of springs from different groups and extending from said slots, closing said mold and injecting rubber under pressure in the vicinity of said holes to bond said pins and fiexure springs to said interior and external surfaces, vulcanizing said rubber within said mold,

removing the bonding parts from said mold and stripping any excess rubber therefrom,

removing said shim metal and cutting said pins apart between successive print hammers,

and machining off pin portions protruding from said print hammers and from said base.

5. The method of claim 4 wherein said mold and base including cooperating positioning means, and further comprising the step of accurately locating said base within said mold by the use of said positioning means.

6. The method of fabricating a print hammer module comprising a pair of spaced print hammers each supported by a pair of substantially rectangular fiexure springs on a common base, comprising the steps of fabricating each of said print hammers and said base with a pair of transverse holes and corresponding slots mutually spaced along the length of each part and extending the width thereof, each of said slots communicating between the corresponding hole and an external surface and having parallel walls spaced from each other a distance less than the diameter of said hole, said base further including a threaded bore,

positioning said fiexure springs in groups of two disposed in parallel planes with the upper and lower spring ends respectively arranged between the flat surfaces of a pair of Wires of substantially semicircular cross-section, said spring ends being spaced along the length of said wires in accordance with the desired print hammer spacing,

soldering said spring ends to said wires to form common parallel pins joining opposite ends of each group of said spaced fiexure springs and protruding from both sides thereof,

coating said external surface, the interior surfaces of said holes and slots, said pins and the end portions of said fiexure springs with a rubber-adhesive substance,

inserting both pairs of springs in an injection mold adapted to accept a cover at one side, said mold and said cover having aligned bores for accurately locating said pins, said mold further including a threaded bore corresponding to said threaded bore in said base and further comprising cavities for accepting said base, said print hammers and said flexure springs respectively, the cavities for said fiexure springs being enlarged in the vicinity of said base and print hammer cavities,

placing said base into said mold by sliding its pair of holes and corresponding slots over the appropriate pins and springs respectively,

positioning said base within said mold by means of a screw engaging both said threaded bores,

placing one of said print hammers into said mold by sliding its pair of holes and corresponding slots over corresponding pins and springs respectively to a position where said hammer is aligned with a pair of fiexure springs of different groups extending through said slots,

positioning a shim in said mold adjacent said one print hammer,

placing the other print hammer into said mold substantially like said one hammer to a position adjacent said shim Where the other pair of springs of said different groups extend through said slots in alignment With said other print hammer,

closing said mold and injecting rubber under pressure in the vicinity of said holes to bond said pins and springs to said external surfaces and to the interior surface of said holes, slots,

vulcanizing said rubber within said mold,

removing the bonded parts from said mold and stripping off any excess rubber,

removing said shim and sawing said pins apart between said print hammers,

and machining oif protruding pin portions from said print hammers and from said base. 7. The method of mounting a plurality of spaced print hammers on a base by the use of flat flexure means having opposite ends, comprising the steps of fabricating said print hammers and said base respectively with transverse holes and corresponding slots communicating with said holes, said holes and slots running the Width of said base and print hammers respectively, arranging said flexure means in two parallel planes, attaching said opposite ends of the fiexure means in each plane to a pair of parallel pins each having a predetermined length greater than said base Width,

coating said holes, slots, pins and the end portions of said flexure means with a rubber-adhesive substance,

positioning said pins in an injection mold having bores for accurately locating the same and further including preformed cavities for accepting said attached flexure means, said base and said print hammers,

positioning said base in said mold by passing the holes and slots thereof over said pins and fleXure means respectively,

successively positioning said print hammers in said mold by passing the holes thereof over said pins, said last-recited step further including interleaving said print hammers with shim spacers inserted in said mold to determine the mutual hammer spacing,

injecting rubber under pressure into said mold in the vicinity of said holes to bond said pins and flexure means to said holes and slots,

vulcanizing said rubber,

removing the bonded parts from said mold and cutting said pins apart between successive print hammers,

and machining 01f portions of said pins protruding from said hammers and said base.

8. The method of claim to said pins includes the steps of ROBERT F. WHITE, T. J. CARVIS, Assistant Examiner.

positioning said ends between the flat surfaces of a pair of wires of substantially semicircular cross-section,

and soldering said ends to said wire pairs to form said pair of parallel pins.

References Cited UNITED STATES PATENTS 2,407,559 9/1946 Krotz 264262 X 2,774,135 12/1956 Morin 29528 X 2,810,301 10/1957 Mat-hues 264275 X 3,078,498 2/1963 Morgan 264262 X 3,144,821 8/1964 Drejza 10193 3,172,352 3/1965 Helms 10193 Primary Examiner.

7 wherein the step of attach- I ing the opposite ends of said flexure means in each plane 

4. THE METHOD OF MOUNTING A PLURALITY OF SPACED PRINT HAMMERS ON A SINGLE BASE, EACH HAMMER BEING SUPPORTED ON A PAIR OF FLAT FLEXURE SPRINGS, COMPRISING THE STEPS OF FABRICATING EACH OF SAID PRINT HAMMERS AND SAID BASE WITH A PAIR OF SPACED HOLES AND WITH CORRESPONDING SLOTS, EACH SLOT HAVING PARALLEL WALLS AND COMMUNICATING BETWEEN AN EXTERNAL SURFACE AND A HOLE, SAID HOLES AND COMMUNICATING SLOTS TRAVERSING THE WIDTH OF SAID BASE AND PRINT HAMMERS RESPECTIVELY, ARRANGING SAID FLEXURE SPRINGS IN TWO SUBSTANTIALLY IDENTICAL GROUPS EACH POSITIONED IN A PLANE SPACED IN ACCORDANCE WITH THE DESIRED SPACING OF SAID PRINT HAMMERS AND WITH THEIR CORRESPONDING ENDS ALIGNED, POSITIONING EACH SET OF CORRESPONDING SPRING ENDS IN EACH PLANE BETWEEN THE FLAT SURFACES OF A PAIR OF WIRES OF SUBSTANTIALLY SIMICIRCULAR CROSS-SECTION, EACH OF SAID WIRES HAVING A PREDETERMINED LENGTH IN EXCESS OF THE WIDTH OF SAID BASE, SOLDERING EACH SET OF SPRING ENDS TO SAID WIRE PAIRS TO FORM A PAIR OF PARALLEL PINS CONNECTING OPPOSITE ENDS IN EACH GROUP OF SPRINGS PAINTING SAID EXTERNAL SURFACE, THE INTERIOR SURFACES OF SAID HOLES AND SLOTS, SAID PINS AND THE END PORTIONS OF SAID FLEXURE SPRINGS WITH A RUBBER-ADHESIVE COMPOUND, INSERTING EACH OF SAID GROUPS IN AN INJECTION MOLD OPENING TO ONE SIDE, SAID MOLD HAVING BORES FOR ACCURATELY LOCATING SAID PINS AND FURTHER INCLUDING PREFORMED CAVITIES FOR ACCEPTING SAID BASE, SAID PRINT HAMMERS AND SAID FLEXURE SPRINGS RESPECTIVELY, THE CAVITIES FOR SAID FLEXURE SPRINGS MERGING INTO SAID BASE AND PRINT HAMMER CAVITIES RESPECTIVELY, PLACING SAID BASE IN SAID MOLD BY SLIDING ITS PAIR OF HOLES AND CORRESPONDING SLOTS OVER THE APPROPRIATE PINS AND SPRINGS RESPECTIVELY TO A POSITION WHERE SAID FLEXURE SPRINGS EXTEND FROM SAID SLOTS, PLACING SAID PRINT HAMMERS IN SAID MOLD INTERLEAVED WITH SHIM METAL SPACERS BY SLIDING EACH PAIR OF PRINT HAMMER HOLES AND THE CORRESPONDING SLOTS OVER APPROPRIATE PINS AND SPRINGS RESPECTIVELY TO A POSITION WHERE EACH HAMMER IS ALIGNED WITH A PAIR OF SPRINGS FROM DIFFERENT GROUPS AND EXTENDING FROM SAID SLOTS, CLOSING SAID MOLD AND INJECTING RUBBER UNDER PRESSURE IN THE VICINITY OF SAID HOLES TO BOND SAID PINS AND FLEXURE SPRINGS TO SAID INTERIOR AND EXTERNAL SURFACES. VULCANIZING SAID RUBBER WITHIN SAID MOLD, REMOVING THE BONDING PARTS FROM SAID MOLD AND STRIPPING ANY EXCESS RUBBER THEREFROM, REMOVING SAID SHIM METAL AND CUTTING SAID PINS APART BETWEEN SUCCESSIVE PRINT HAMMERS, AND MACHINING OFF PIN PORTIONS PROTRUDING FROM SAID PRINT HAMMERS AND FROM SAID BASE. 